A time intensity curve is provided as an index effective for diagnosis, which represents a temporal change in the luminance value or luminance average of a region of interest set on a two-dimensional ultrasonic image. An operator sets a region of interest by moving, for example, a circular, quadrilateral, or polygonal ROI marker to the region of interest on a two-dimensional ultrasonic image with a mouse or trackball.
It is more difficult to align an ROI marker with a portion of interest on a three-dimensional ultrasonic image than on a two-dimensional ultrasonic image.